Solar-sail propulsion · Est. 2031 · Low Earth Orbit → Sunward

We sail
on light.

Perihelion builds spacecraft that carry no fuel. A square kilometre of mirror-thin film, pushed by the raw pressure of sunlight — accelerating, forever, toward the star.

See the physics The craft
01 The mission

Every rocket carries
its own weight in fuel.
We left the tank behind.

Chemical propulsion is a bargain with diminishing returns: to go faster you burn more, and to burn more you must first carry it, which makes you heavier, which means you burn more still.

Light has no such tax. Sunlight exerts a real, measurable pressure on any surface it strikes — about nine micronewtons per square metre at Earth's distance. Vanishingly small. But it never stops, it costs nothing, and over months it compounds into velocities no chemical stage can reach.

Perihelion designs the sails, the booms, and the flight software to harvest that pressure — spacecraft that get lighter as they get faster, and never run out.

  • 0 kgpropellant carried
  • 1.0 km²deployed sail area
  • ~8.6 Nthrust at 1 AU
  • ∞burn duration
02 The craft · HELIOS-1

A mirror, four booms,
and almost nothing else.

Cutaway diagram of the HELIOS-1 solar sail: a square reflective membrane tensioned by four diagonal booms from a central bus. 2.5 µm film aluminised polyimide CFRP boom 4 × 710 m deployable avionics bus
HELIOS-1 · 1.0 km² four-quadrant square rigger. Total dry mass 7,850 kg.

Specification

Sail area
1.0 km² (1000 × 1000 m)
Membrane
2.5 µm aluminised polyimide
Reflectivity
0.90 specular
Areal density
7.85 g/m² (film + structure)
Booms
4 × 710 m CFRP, roll-deployed
Dry mass
7,850 kg
Char. acceleration
1.10 mm/s² @ 1 AU
Attitude
3-axis, sliding-mass trim + reaction wheels

Deployment is the hardest hour of the mission: a folded package the size of a shipping container unrolls into a mirror a kilometre on each side, held flat to within a few centimetres.

03 The physics · radiation pressure

Light has momentum.
A mirror doubles it.

A photon carries momentum p = E/c. When it is absorbed, it delivers that momentum to the surface. When it is reflected, it hands over twice as much — arriving and leaving. A solar sail is, at heart, the biggest, lightest mirror we can fly, angled to steal momentum from every photon that hits it.

Thrust model

Adjust the sail and see the numbers a flight engineer actually cares about.

Solar flux1361W/m²
Radiation pressure8.62µN/m²
Thrust8.63N
Characteristic accel1.10mm/s²
Δv after 30 days2.85km/s
Time to 50 km/s526days

ac = 2 · η · (L☉ / 4πr²c) · A / m  ·  the whole company, in one line

04 The people & the backers

Built by people who have
flown hardware before.

Dr. Ingrid Vӧss

Founder · Flight dynamics

Trajectory lead on two interplanetary missions. Wrote the sliding-mass attitude control that lets a sail steer without spending anything.

Rafael Okonkwo

Membranes & deployment

Fifteen years folding things that must unfold perfectly in vacuum. Holds four patents on rip-stop coating and roll geometry.

Mei Chen

Flight software

Built the guidance stack. Believes a sail should fly itself for six months without a single command from the ground.

Backed by

  • Helios Ventures
  • Kármán Line Capital
  • The Planetary Endowment
  • Orbit Foundry
  • Lagrange Partners

Now hiring · Seed round open

Come help us catch
the light.

We are looking for membrane engineers, GN&C specialists, and the kind of people who read a datasheet for fun. First flight is closer than you think.